U.S. patent application number 11/794658 was filed with the patent office on 2008-08-21 for exhaust gas purification system for internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Takeshi Hashizume.
Application Number | 20080196395 11/794658 |
Document ID | / |
Family ID | 39705481 |
Filed Date | 2008-08-21 |
United States Patent
Application |
20080196395 |
Kind Code |
A1 |
Hashizume; Takeshi |
August 21, 2008 |
Exhaust Gas Purification System For Internal Combustion Engine
Abstract
The present invention is directed to an exhaust gas purification
system for an internal combustion engine that performs high
pressure PM filter regeneration process by decreasing the degree of
opening of an exhaust throttle valve in regenerating the
particulate matter trapping capacity of a particulate filter and
has as an object to provide a technology that enables to perform
the high pressure PM filter regeneration process while suppressing
excessive temperature rise of the particulate filter even while the
vehicle is moving. According to the invention, a prediction is
made, when the high pressure PM filter regeneration process is
performed, as to whether there is a possibility that the
temperature of the particulate filter will reach a predetermined
upper limit temperature, and the pressure inside the particulate
filter is controlled in accordance with the prediction.
Inventors: |
Hashizume; Takeshi;
(Shizuoka-ken, JP) |
Correspondence
Address: |
KENYON & KENYON LLP
1500 K STREET N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
TOYOTA-SHI AICHI
JP
|
Family ID: |
39705481 |
Appl. No.: |
11/794658 |
Filed: |
May 12, 2006 |
PCT Filed: |
May 12, 2006 |
PCT NO: |
PCT/JP06/09979 |
371 Date: |
July 3, 2007 |
Current U.S.
Class: |
60/295 ;
60/286 |
Current CPC
Class: |
F01N 2560/08 20130101;
Y02T 10/40 20130101; F02B 37/00 20130101; F01N 3/0235 20130101;
F01N 3/023 20130101; F01N 2260/12 20130101; F01N 2260/14 20130101;
F02D 41/123 20130101; Y02T 10/47 20130101; F01N 2240/36 20130101;
F02D 2200/0804 20130101; F01N 9/002 20130101; F02D 41/029
20130101 |
Class at
Publication: |
60/295 ;
60/286 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2005 |
JP |
2005-145495 |
Claims
1. An exhaust gas purification system for an internal combustion
engine comprising: a particulate filter for trapping particulate
matter contained in exhaust gas; an exhaust throttle valve provided
in an exhaust passage downstream of said particulate filter; a PM
filter regeneration device that performs a PM filter regeneration
process for oxidizing and removing particulate matter trapped on
said particulate filter; a pressure increasing device for
increasing the pressure inside the particulate filter by decreasing
the degree of opening of said exhaust throttle valve when said PM
filter regeneration process is performed; a prediction device for
making a prediction as to whether or not there is a possibility
that the temperature of said particulate filter reaches an upper
limit value, when the pressure inside said particulate filter has
been increased by said pressure increasing device; and a pressure
decreasing device for decreasing the pressure inside said
particulate filter when it is predicted by said prediction device
that there is a possibility that the temperature of said
particulate filter reaches the upper limit value.
2. An exhaust gas purification system for an internal combustion
engine according to claim 1, wherein the smaller the quantity of
the exhaust gas flowing into said particulate filter is, the lower
the pressure inside said particulate filter is made by said
pressure decreasing device.
3. An exhaust gas purification system for an internal combustion
engine according to claim 1, wherein the higher the temperature of
the particulate filter is, the lower the pressure inside said
particulate filter is made by said pressure decreasing device.
4. An exhaust gas purification system for an internal combustion
engine according to claim 1, wherein the larger the amount of
particulate matter trapped on said particulate filter is, the lower
the pressure inside said particulate filter is made by said
pressure decreasing device.
5. An exhaust gas purification system for an internal combustion
engine according to claim 1, wherein the higher the load of said
internal combustion engine is, the lower the pressure inside said
particulate filter is made by said pressure decreasing device.
6. An exhaust gas purification system for an internal combustion
engine according to claim 1, wherein when it is predicted by said
prediction device that there is a possibility that the temperature
of said particulate filter reaches the upper limit value, said
pressure decreasing device stops increasing of the pressure inside
said particulate filter by said pressure increasing device.
7. An exhaust gas purification system for an internal combustion
engine according to claim 6, said pressure decreasing device stops
increasing of the pressure inside said particulate filter by said
pressure increasing device on condition that at least one of the
quantity of exhaust gas flowing into the particulate filter, the
temperature of said particulate filter, the amount of particulate
matter trapped on said particulate filter and the load of said
internal combustion engine at the time when it is predicted by said
prediction device that there is a possibility that the temperature
of said particulate filter reaches the upper limit value falls out
of a predetermined allowable range.
8. An exhaust gas purification system for an internal combustion
engine according to claim 1 further comprising an estimation device
for estimating the amount of particulate matter remaining on said
particulate filter while the PM filter regeneration process is
performed, wherein the smaller the amount of particulate matter
estimated by said estimation device becomes, the higher the
pressure inside said particulate filter is made by said pressure
decreasing device.
9. An exhaust gas purification system for an internal combustion
engine according to claim 8, wherein said estimation device
estimates the amount of particulate matter remaining on said
particulate filter using, as parameters, the temperature of said
particulate filter, the quantity of exhaust gas flowing into said
particulate filter and the pressure inside said particulate
filter.
10. An exhaust gas purification system for an internal combustion
engine according to claim 1 further comprising a fuel injection
device that is adapted to continue, when a running condition of
said internal combustion engine enters a region in which fuel cut
is to be effected while the degree of opening of said exhaust
throttle valve has been decreased by said pressure increasing
device, a predetermined quantity of fuel injection, wherein the
higher the pressure inside said particulate filter is, the larger
said predetermined quantity is made.
11. An exhaust gas purification system for an internal combustion
engine according to claim 1, wherein said pressure decreasing
device decreases the pressure inside said particulate filter by
increasing the degree of opening of said exhaust throttle
valve.
12. An exhaust gas purification system for an internal combustion
engine according to claim 1 further comprising: a flow rate
regulation valve provided in an exhaust passage upstream of said
particulate filter; and an exhaust brake device for activating
exhaust brake by decreasing the degree of opening of said exhaust
throttle valve or said flow rate regulation valve, wherein upon
activating exhaust brake while the PM filter regeneration process
is performed, said exhaust brake device decreases the degree of
opening of said flow rate regulation valve if it is predicted by
said prediction device that there is a possibility that the
temperature of said particulate filter reached said upper limit
temperature, and decreases the degree of opening of said exhaust
throttle valve if it is predicted by said prediction device that
there is no possibility that the temperature of said particulate
filter reaches said upper limit temperature.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a technology for
regenerating the particulate matter (PM) trapping capacity of a
particulate filter.
BACKGROUND OF THE INVENTION
[0002] Japanese Patent Application Laid-Open NO. 2001-317333
discloses a process of regenerating the PM trapping capacity of a
particulate filter while increasing the pressure inside the
particulate filter by decreasing the degree of opening of an
exhaust throttle valve provided in an exhaust passage downstream of
the particulate filter (which process will be hereinafter referred
to as the high pressure PM filter regeneration process). Japanese
Utility Model Application Laid-Open No. 4-008718 and Japanese
Patent Application Laid-Open No. 2003-120263 also disclose
technologies related to regeneration of the PM trapping capacity of
a particulate filter.
SUMMARY OF THE INVENTION
[0003] If the high pressure PM filter regeneration process is
performed while running conditions of the internal combustion
engine are varying every second as is the case when the vehicle
equipped with that engine is moving, it is highly likely that the
temperature of the particulate filter rises excessively. For this
reason, it has been difficult to perform the high pressure PM
filter regeneration process while the vehicle is moving.
[0004] The present invention has been made in view of the above
described circumstances and has as an object to provide a technique
to perform the high pressure PM filter regeneration process while
suppressing excessive temperature rise of a particulate filter in
an exhaust gas purification system for an internal combustion
engine that is adapted to perform the high pressure PM filter
regeneration process, even during the time in which running
conditions of the internal combustion engine can easily change as
is the case when the vehicle is moving.
[0005] To achieve the above object, according to the present
invention, in an exhaust gas purification system for an internal
combustion engine that is adapted to the perform high pressure PM
filter regeneration process by increasing the pressure inside the
particulate filter to regenerate its PM trapping capacity, a
prediction is made as to whether or not there is a possibility that
the temperature of the particulate filter will reach a
predetermined upper limit temperature when the high pressure
regeneration process is performed. The pressure inside the
particulate filter is controlled based on the result of this
prediction thereby making it possible to perform the high pressure
PM filter regeneration process while preventing excessive
temperature rise of the particulate filter even during the time in
which running conditions of the internal combustion engine can
easily change as is the case when the vehicle is moving.
[0006] Specifically, an exhaust gas purification system for an
internal combustion engine according to the present invention
comprises a particulate filter that traps particulate matter
contained in the exhaust gas, an exhaust throttle valve provided in
an exhaust passage downstream of the particulate filter, a PM
filter regeneration device for performing PM filter regeneration
process to oxidate and remove particulate matter trapped on the
particulate filter, a pressure increasing device for increasing the
pressure inside the particulate filter by decreasing the degree of
opening of the exhaust throttle valve when the PM filter
regeneration process is performed, a prediction device for
predicting whether or not there is a possibility that the
temperature of the particulate filter will reach an upper limit
value when the pressure inside the particulate filter is increased
by the pressure increasing device, and a pressure decreasing device
for decreasing the pressure inside the particulate filter if it is
predicted by the prediction means that there is a possibility that
the temperature of the particulate filter will reach the upper
limit value.
[0007] The pressure increasing device is adapted to reduce the
degree of opening of the exhaust throttle valve while the PM filter
regeneration process is performed to increase the pressure (the
partial pressure of oxygen) inside the particulate filter. If the
PM filter regeneration process is performed in the state in which
the pressure inside the particulate filter has been increased (the
high pressure PM filter regeneration process), the time required
for the PM filter regeneration process can be made shorter, since
the reaction rate in oxidation of the particulate matter is
enhanced.
[0008] Since the quantity of heat of oxidation reaction generated
per unit time increases with an increase in the rate of the
oxidation reaction of particulate matter, the temperature of the
particulate filter tends to become higher during the high pressure
PM filter regeneration process than during the normal PM filter
regeneration process (that is, the PM filter regeneration process
that is performed without decreasing the degree of opening of the
exhaust throttle valve). Especially when running conditions of the
internal combustion engine can easily change as is the case when
the vehicle is moving, it is highly likely that changes in the
amount and/or temperature of the exhaust gas causes an excessive
rise in the temperature of the particulate filter. For this reason,
it has been difficult to perform the high pressure PM filter
regeneration process while the vehicle is moving.
[0009] In view of the above, in the exhaust gas purification system
according to the present invention, while the high pressure PM
filter regeneration process is being performed, a prediction is
made by the prediction device as to whether or not there is a
possibility that the temperature of the particulate filter will
reach an predetermined upper limit temperature. This upper limit
temperature may be the temperature at which the particulate filter
starts to deteriorate due to heat. However, in order to prevent
such thermal deterioration of the particulate filter for sure, it
is preferred that the upper limit temperature be set lower than the
temperature at which the particulate filter starts to deteriorate
due to heat. Here, the deterioration of the particulate filter due
to heat refers to not only thermal deterioration of the particulate
filter itself but also thermal deterioration of the catalyst or
other elements supported on or annexed to the particulate
filter.
[0010] If it is predicted by the prediction device that there is a
possibility that the temperature of the particulate filter will
reach the aforementioned upper limit value, the pressure decreasing
device functions to decrease the pressure inside the particulate
filter. This causes a decrease in the rate of oxidation reaction of
particulate matter in the particulate filter, and the quantity of
heat generated by oxidative reaction of per unit time decreases
accordingly. Therefore, the temperature of the particulate filter
is hard to reach the upper limit temperature.
[0011] By decreasing the pressure inside the particulate filter
when it is predicted that there is a possibility that the
temperature of the particulate filter will reach the upper limit
temperature in the above described manner, excessive temperature
rise of the particulate filter can be prevented even if the high
pressure PM filter regeneration process is performed during the
time in which running conditions of the internal combustion engine
can easily change as is the case when the vehicle is moving.
Therefore, it is possible to enlarge the range of running
conditions in which the high pressure PM filter regeneration
process is allowed to be performed.
[0012] In making a prediction as to whether or not there is a
possibility that the temperature of the particulate filter will
reach the upper limit temperature in the present invention, it may
be determined that there is a possibility that the temperature of
the particulate filter will reach the upper limit temperature, for
example, when at least one of the following conditions is met: 1)
the quantity of the exhaust gas flowing into the particulate filter
is small; 2) the temperature of the particulate filter itself is
close to the upper limit temperature; 3) the amount of the
particulate matter trapped on the particulate filter (or the amount
of the particulate matter remaining on the particulate filter) is
large.
[0013] In the present invention, the method of decreasing the
pressure inside the particulate filter may be, for example, to
increase the degree of opening of the exhaust throttle valve, to
decrease the degree of opening of the intake throttle valve, to
increase the quantity of the EGR gas recirculated from the exhaust
passage in the upstream of the particulate filter to the intake
passage, to enlarge the volume of a variable volume turbocharger,
or to increase the quantity of the exhaust gas flowing into a
bypass passage that detours around the particulate filter, etc.
[0014] In the present invention, the pressure decreasing device may
be adapted to stop the high pressure PM filter regeneration process
(namely to release the high pressure state inside the particulate
filter realized by the pressure increasing device) immediately when
it is predicted that there is a possibility that the temperature of
the particulate filter will reach the upper limit temperature.
[0015] If the high pressure PM filter regeneration process is
stopped at the time when it is predicted that there is a
possibility that the temperature of the particulate filter will
reach the upper limit temperature, the pressure inside the
particulate filter falls steeply. Therefore, it is easy to prevent
excessive temperature rise of the particulate filter.
[0016] After the high pressure PM filter regeneration process is
stopped, the PM filter regeneration process may be terminated
entirely, or, alternatively, normal PM filter regeneration process
may be continued.
[0017] On the other hand, the pressure decreasing device in the
present invention may be adapted in such a way that it does not
stop the high pressure PM filter regeneration process immediately
when it is predicted by the prediction device that there is a
possibility that the temperature of the particulate filter will
reach the upper limit temperature, but continues the high pressure
PM filter regeneration process while decreasing the pressure inside
the particulate filter.
[0018] In that case, in decreasing the pressure inside the
particulate filter, the pressure decreasing device may use as a
parameter(s) at least one of the quantity of the exhaust gas
flowing into the particulate filter, the temperature of the
particulate filter itself, the amount of the particulate matter
trapped on the particulate filter and the load of the internal
combustion engine.
[0019] When the quantity of the exhaust gas flowing into the
particulate filter becomes smaller, the quantity of heat carried
away from the particulate filter by the exhaust gas decreases.
Accordingly, the temperature of the particulate filter is likely to
rise.
[0020] However, if the pressure inside the particulate filter is
decreased as the quantity of the exhaust gas flowing into the
particulate filter becomes smaller, it is possible to continue the
high pressure PM filter regeneration process while reducing the
possibility that the temperature of the particulate filter rises to
the upper limit temperature.
[0021] The higher the temperature of the particulate filter itself
is, the higher the rate of oxidation reaction of the particulate
matter trapped on the particulate filter is, and the more the
temperature of the particulate filter is likely to rise
accordingly. In addition, when the temperature of the particulate
filter becomes high, the possibility that the temperature of the
particulate filter is raised to the upper limit temperature by a
small quantity of heat generated by oxidation reaction arises.
[0022] However, if the pressure inside the particulate filter is
decreased as the temperature of the particulate filter itself
becomes higher, it is possible to continue the high pressure PM
filter regeneration process while reducing the possibility that the
temperature of the particulate filter rises to the upper limit
temperature.
[0023] The larger the amount of the particulate matter trapped on
(or remaining on) the particulate filter is, the larger the
quantity of particulate matter that is oxidized per unit time
becomes. Accordingly, the quantity of heat generated by oxidation
reaction per unit time becomes larger, and the temperature of the
particulate filter is likely to rise.
[0024] However, if the pressure inside the particulate filter is
decreased as the amount of the particulate matter trapped on the
particulate filter increases, it is possible to continue the high
pressure PM filter regeneration process while reducing the
possibility that the temperature of the particulate filter rises to
the upper limit temperature.
[0025] The higher the load of the internal combustion engine is,
the higher the temperature of the exhaust gas flowing into the
particulate filter becomes. An increase in the temperature of the
exhaust gas flowing into the particulate filter leads to an
increase in the quantity of heat transferred from the exhaust gas
to the particulate filter, which in turn leads to a decrease in the
quantity of heat transferred from the particulate filter to the
exhaust gas. Accordingly, the temperature of the particulate filter
is likely to rise.
[0026] However, if the pressure inside the particulate filter is
made lower as the load of the internal combustion engine becomes
higher, it is possible to continue the high pressure PM filter
regeneration process while reducing the possibility that the
temperature of the particulate filter rises to the upper limit
temperature.
[0027] In the case where, at the time at which it is predicted by
the prediction device that there is a possibility that the
temperature of the particulate filter will reach the upper limit
temperature, the quantity of the exhaust gas flowing into the
particulate filter is excessively small, the temperature of the
particulate filter itself reaches nearly the upper limit
temperature, or the amount of the particulate matter trapped on the
particulate filter is excessively large, it is highly likely that
the temperature of the particulate filter reaches the upper limit
temperature if the temperature of the particulate filter has risen
close to the upper limit temperature. In such cases, the high
pressure PM filter regeneration process may be stopped (namely, the
high pressure state inside the particulate filter realized by the
pressure increasing device may be released) immediately.
[0028] If the degree of opening of the exhaust throttle valve is
small when the load of the internal combustion engine is relatively
high, there is a possibility that the drivability is deteriorated
as well as a possibility that the temperature of the particulate
filter reaches the upper limit temperature. In view of this, the
high pressure PM filter regeneration process may be stopped
(namely, the high pressure state inside the particulate filter
realized by the pressure increasing device may be released) when
the load of the internal combustion engine exceeds a predetermined
load.
[0029] The exhaust gas purification system according to the present
invention may be further provided with an estimation device for
estimating the amount of the particulate matter remaining on the
particulate filter while the PM filter regeneration process is
performed. In this case, the pressure decreasing device may be
adapted to increase the pressure inside the particulate filter as
the amount of the particulate matter estimated by the estimation
device becomes smaller.
[0030] As the amount of the particulate matter remaining on the
particulate filter decreases, the quantity of oxidation heat
generated by oxidation of the particulate matter per unit time also
decreases. If the pressure inside the particulate filter is
increased as the amount of the particulate matter remaining on the
particulate filter decreases, it is possible to continue the high
pressure PM filter regeneration process while reducing the
possibility that the temperature of the particulate filter rises to
the upper limit temperature.
[0031] One method of estimating the amount of the particulate
matter remaining on the particulate filter while the PM filter
regeneration process is performed is to estimate the quantity of
particulate matter that is oxidized per unit time (or the PM
oxidization rate) based on, as parameters, the temperature of the
particulate filter and the quantity of the exhaust gas flowing into
the particulate filter and to determine the amount of the remaining
particulate matter based on a value obtained by that estimation and
the time over which the PM filter regeneration process has been
performed.
[0032] However, the quantity of particulate matter oxidized per
unit time changes depending on the pressure inside the particulate
filter. In view of this, in the present invention, the estimation
device is designed to estimate the amount of the particulate matter
remaining on the particulate filter taking into consideration also
the pressure inside the particulate filter in addition to the
temperature of the particulate filter and the quantity of the
exhaust gas flowing into the particulate filter.
[0033] By the above described method, it is possible to estimate
the amount of the particulate matter remaining on the particulate
filter accurately. Therefore, it is also possible to adjust the
pressure inside the particulate filter to a pressure that is
suitable for the actual amount of the remaining particulate matter
when the high pressure PM filter regeneration process is performed,
and to terminate the high pressure PM filter regeneration process
at an appropriate time (for example, at the time when the amount of
remaining particulate matter becomes substantially zero).
[0034] The exhaust gas purification system according to the present
invention may be provided with fuel injection device that continues
to inject a predetermined quantity of fuel without effecting fuel
cut even if the running condition of the internal combustion engine
enters the region in which fuel cut is to be effected while the
high pressure PM filter regeneration process is being
performed.
[0035] Since the degree of opening of the exhaust throttle valve is
made small while the high pressure PM filter regeneration process
is performed, performing fuel cut may lead to deterioration in the
drivability. More specifically, when the degree of opening of the
exhaust throttle valve is made small, the exhaust gas pressure
acting on the internal combustion is high, and therefore frictions
in the internal combustion engine are large. If fuel injection is
stopped under such a situation, there is a possibility that
unnecessary strong braking force (so-called exhaust brake) acts on
the internal combustion engine to deteriorate the drivability.
[0036] If a predetermined quantity of fuel injection is continued
without effecting fuel cut when the running condition of the
internal combustion engine enters the region in which fuel cut is
to be effected while the high pressure PM filter regeneration
process is performed, a torque counteracting the exhaust brake is
created. Thus, deterioration in drivability can be prevented.
Furthermore, the predetermined quantity of fuel injection helps to
keep the exhaust gas temperature high. Therefore, an additional
advantageous effect that the high pressure PM filter regeneration
process is continued even in the running condition in which fuel
cut is to be effected.
[0037] In view of the fact that the braking force acting on the
internal combustion engine increases with an increase in the higher
the pressure inside the particulate filter, the higher the pressure
inside the filter is, the larger the aforementioned predetermined
quantity may be made.
[0038] By increasing or decreasing the fuel injection quantity in
proportion to the pressure inside the particulate filter as
described above, it is possible to generate a torque proportional
to the braking force. Thus, it is possible to prevent deterioration
in the drivability even when the braking force acting on the
internal combustion engine changes.
[0039] There may be cases where activation of exhaust brake is
requested while the high pressure PM filter regeneration process is
being performed. If the degree of opening of the exhaust throttle
valve is further decreased when such a request is made, there is a
possibility that the pressure inside the particulate filter becomes
excessively high to cause an excessive temperature rise of the
particulate filter.
[0040] In view of this, in the exhaust gas purification system
according to the present invention, a flow rate regulation valve
may be provided in the exhaust passage upstream of the particulate
filter, and in addition exhaust brake means for activating exhaust
brake by decreasing either the degree of opening of the exhaust
throttle valve or the flow rate regulation valve may also be
provided.
[0041] When a request for activating exhaust brake is made while
the high pressure PM filter regeneration process is being
performed, the exhaust brake device selectively determines which of
the exhaust throttle valve and the flow rate regulation valve is to
be used to activate exhaust brake depending on the result of
prediction by the prediction device.
[0042] For example, in the case where it is predicted by the
prediction device that there is a possibility that the temperature
of the particulate filter will reach the upper limit temperature,
the exhaust brake device activates exhaust brake by decreasing the
degree of opening of the flow rate regulation valve.
[0043] If this is done, the exhaust gas pressure in the upstream of
the flow rate regulation valve increases, and the exhaust gas
pressure in the downstream of it decreases. Accordingly, it is
possible to increase the exhaust gas pressure acting on the
internal combustion engine while reducing the pressure inside the
particulate filter. Consequently, it is possible to activate
exhaust brake while suppressing excessive temperature rise of the
particulate filter.
[0044] On the other hand, in the case where it is predicted by the
prediction device that there is no possibility that the temperature
of the particulate filter will reach the upper limit temperature,
the exhaust brake device activates exhaust brake by decreasing the
degree of opening of the exhaust throttle valve.
[0045] If this is done, the exhaust gas pressure in the upstream of
the exhaust throttle valve increases, and therefore, it is possible
to increase the exhaust gas pressure acting on the internal
combustion engine while increasing the pressure inside the
particulate filter. Consequently, it is possible to activate
exhaust brake and regenerate the particulate matter trapping
capacity of the particulate filter earlier.
[0046] In connection with the above, when a request for activating
exhaust brake is made while the high pressure PM filter
regeneration process is being performed, the exhaust brake device
may activate exhaust brake by decreasing the degree of opening of
the flow rate regulation valve irrespective of the result of
prediction by the prediction device.
[0047] The above and other objects, features and advantages of the
present invention will become more readily apparent to those
skilled in the art from the following detailed description of
preferred embodiments of the present invention taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] FIG. 1 is a diagram schematically showing the structure of
the internal combustion engine.
[0049] FIG. 2 is a map used in determining a basic target
pressure.
[0050] FIG. 3 is a map used in determining a pressure correction
coefficient.
[0051] FIG. 4 is a map used in determining a temperature correction
coefficient.
[0052] FIG. 5 is a map used in determining a load correction
coefficient.
[0053] FIG. 6 is a graph showing a high pressure PM filter
regeneration process prohibition region that is determined
depending on the inflowing exhaust gas quantity, the remaining PM
amount and the filter temperature.
[0054] FIG. 7 is a graph showing a high pressure PM filter
regeneration process prohibition region that is determined
depending on the engine load and the engine speed.
[0055] FIG. 8 is a map used in determining the fuel injection
quantity in the state in which fuel cut is to be effected.
[0056] FIG. 9 is a flow chart of a high pressure regeneration
routine in the first embodiment.
[0057] FIG. 10 is a flow chart of a remaining PM amount calculation
routine in the first embodiment.
[0058] FIG. 11 is a flow chart of a fuel cut control routine in the
first embodiment.
[0059] FIG. 12 is a map used in determining a degree of opening
correction amount for the exhaust throttle valve.
[0060] FIG. 13 is a diagram schematically showing the structure of
the internal combustion engine according to a second
embodiment.
[0061] FIG. 14 is a graph showing a region in which reduction of
the degree of opening of the exhaust throttle valve is prohibited,
the region being determined based on the inflowing exhaust gas
quantity and the remaining PM amount.
[0062] FIG. 15 is a flow chart of an exhaust brake control routine
in the second embodiment.
DETAILED DESCRIPTION
[0063] In the following, specific embodiments of the present
invention will be described with reference to the accompanying
drawings.
First Embodiment
[0064] A first embodiment of the present invention will be
described with reference to FIGS. 1 through 12. FIG. 1 is a diagram
schematically showing the structure of an internal combustion
engine to which the present invention is applied.
[0065] The internal combustion engine 1 shown in FIG. 1 is a
compression ignition type internal combustion engine that is driven
using light oil as fuel (i.e. a diesel engine). The internal
combustion engine 1 has a plurality of cylinders 2, each of which
is provided with a fuel injection valve 3 that injects fuel
directly into the cylinder 2.
[0066] The internal combustion engine 1 is connected with an intake
passage 4. In the intake passage 4 is provided a compressor housing
50 of a centrifugal supercharger (or a turbocharger) 5. An air flow
meter 6 is provided in the intake passage 4 upstream of the
compressor housing 50. An intake air cooler (i.e. intercooler) 7 is
provided in the intake passage downstream of the compressor housing
50. An intake throttle valve 8 is provided in the intake passage 4
downstream of the intercooler 7.
[0067] The internal combustion engine 1 is connected with an
exhaust passage 9. At certain position in the exhaust passage 9 is
provided a turbine housing 51 of the turbocharger 5. A fuel
addition valve 10 for adding fuel to the exhaust gas flowing in the
exhaust passage 9 is provided in the exhaust passage 9 upstream of
the turbine housing 51. A particulate filter 11 is provided in the
exhaust passage downstream of the turbine housing 51.
[0068] A catalyst having an oxidizing ability is supported on the
base member of the particulate filter 11. The catalyst having an
oxidizing ability may be for example an oxidizing catalyst, a
three-way catalyst or an NOx storage reduction catalyst.
Alternatively, a catalyst having an oxidizing ability may be
provided just upstream of the particulate filter 11 instead of the
oxidizing catalyst having an oxidizing ability supported on the
base member of the particulate filter 11.
[0069] An exhaust throttle valve 12 is provided in the exhaust
passage 9 downstream of the particulate filter 11. An exhaust gas
temperature sensor 13 and an exhaust gas pressure sensor 14 are
provide in the exhaust passage 9 downstream of the particulate
filter 11 and upstream of the exhaust throttle valve 12. In
addition, a pressure difference sensor 15 for detecting the
difference in the exhaust gas pressure between upstream and
downstream of the particulate filter 11 (which will be hereinafter
referred to as the pressure difference across the filter) is also
provided in the exhaust passage 9.
[0070] To the internal combustion engine 1 is annexed an ECU 16.
The ECU 16 is an arithmetic and logic circuit composed of, a CPU, a
ROM, RAM and a backup RAM and other elements. The ECU 16 is
electrically connected with the aforementioned various sensors such
as the air flow meter 6, the exhaust gas temperature sensor 13, the
exhaust gas pressure sensor 14 and the pressure difference sensor
15. The ECU 16 is also electrically connected with the fuel
injection valve 3, the intake throttle valve 8, the fuel addition
valve 10 and the exhaust throttle valve 12.
[0071] In the internal combustion engine 1 having the above
described structure, the ECU 16 is adapted to execute PM filter
regeneration control that constitutes the principal feature of the
present invention as well as various known control such as fuel
injection control.
[0072] In the PM filter regeneration control, a determination is
made by the ECU 16 as to whether or not the amount of the
particulate matter trapped on the particulate filter 11 (or the PM
trapping amount) is larger than a predetermined upper limit amount.
This upper limit amount is set to an amount a little smaller than
the maximum amount of the particulate matter that the particulate
filter 11 can trap.
[0073] In making a determination as to whether or not the PM
trapping amount of the particulate filter 11 has reached the upper
limit amount, it may be determined that the PM trapping amount of
the particulate filter 11 has reached the upper limit amount for
example when one of the following conditions is met: the time
elapsed since the latest previous execution of the PM filter
regeneration process exceeds a predetermined time; the travel
distance of the vehicle after the latest previous execution of the
PM filter regeneration process is larger than a predetermined
distance; and the output signal of the pressure difference sensor
15 is larger than a predetermined value.
[0074] The ECU 16 executes the PM filter regeneration process when
it is determined according to the above described method that the
PM trapping amount of the particulate filter 11 has reached the
upper limit amount. In the PM filter regeneration process, the ECU
16 causes the fuel addition valve 11 to add fuel to the exhaust gas
to raise the temperature of the particulate filter 11 up into a
temperature range that makes it possible to oxidize the particulate
matter. In addition, the ECU 16 controls to decrease the degree of
opening of the exhaust throttle valve 12.
[0075] If the degree of opening of the exhaust throttle valve 12 is
decreased while the PM filter regeneration process is performed,
the pressure inside the particulate filter 11 (the partial pressure
of oxygen) increases. If the PM filter regeneration process is
performed in the state in which the pressure inside the particulate
filter 11 (which will be hereinafter referred to as the in-filter
pressure) has been increased, the rate of oxidation reaction of the
particulate matter trapped on the particulate filter 11 increases,
and therefore it is possible to shorten the execution time of the
PM filter regeneration process.
[0076] As per the above, the pressure increasing means in the
present invention is realized by the ECU 16 in decreasing the
degree of opening of the exhaust throttle valve 12 during the PM
filter regeneration process.
[0077] In connection with the above, since an increase in the rate
of oxidation reaction of the particulate matter leads to an
increase in the quantity of heat generated by the oxidation
reaction of the particulate matter per unit time, the temperature
of the particulate filter 11 is more likely to rise during the high
pressure PM filter regeneration process than during the normal PM
filter regeneration process (that is, PM filter regeneration
process that is performed without decreasing the degree of opening
of the exhaust throttle valve 12).
[0078] Especially when running conditions of the internal
combustion engine 1 can easily change as is the case when the
vehicle is moving, it is highly likely that the temperature of the
particulate filter 11 rises excessively due to changes in the
exhaust gas amount and/or the exhaust gas temperature. This
presents the problem that the running condition that allows to
perform the high pressure PM filter regeneration process is limited
to stationary running conditions such as idling.
[0079] In view of this, in the PM filter regeneration control in
this embodiment, the ECU 16 is adapted to decrease the in-filter
pressure when it is predicted that there is a possibility that the
temperature of the particulate filter 11 (which will be hereinafter
referred to as the filter temperature) will reach a predetermined
upper limit temperature while the high pressure PM filter
regeneration process is performed.
[0080] The aforementioned upper limit temperature is a temperature
a little lower than the temperature that causes thermal
deterioration of the particulate filter 11 or the temperature that
causes the thermal deterioration of the catalyst supported on the
particulate filter 11, whichever is the lower.
[0081] The prediction that there is a possibility that the filter
temperature will reach the upper limit temperature is made for
example when the quantity of the exhaust gas flowing into the
particulate filter 11 (which will be hereinafter referred to as the
inflowing exhaust gas quantity) is small, when the filter
temperature is high, when the amount of the particulate matter
trapped on or remaining on the particulate filter 11 (which will be
hereinafter referred to as the remaining PM amount), and/or when
the load of the internal combustion engine 1 (which will be
hereinafter referred to as the engine load) is high.
[0082] When the inflowing exhaust gas quantity decreases, the
quantity of heat that the exhaust gas takes away from the
particulate filter 11 also decreases. Then, the filter temperature
is likely to rise. This tendency becomes more pronounced as the
inflowing exhaust gas quantity becomes smaller.
[0083] When the filter temperature rises, the rate of oxidation
reaction of the particulate matter trapped on the particulate
filter 11 becomes higher. Then, the filter temperature is likely to
rise. This tendency becomes more pronounced as the filter
temperature becomes higher.
[0084] When the remaining PM amount increases, the quantity of heat
generated by oxidation reaction of the particulate matter per unit
time also increase. Then, the filter temperature is likely to rise.
This tendency becomes more pronounced as the remaining PM amount
increases.
[0085] When the engine load increases, the temperature of the
exhaust gas flowing into the particulate filter 11 rises. The rise
in the temperature of the exhaust gas flowing into the particulate
filter 11 leads to an increase in the quantity of heat transferred
from the exhaust gas to the particulate filter 11 and a decrease in
the quantity of heat transferred from the particulate filter 11 to
the exhaust gas. Then, the filter temperature is likely to rise.
This tendency becomes more pronounced as the engine load becomes
higher.
[0086] From the above follows that it is possible to prevent the
filter temperature to rise to the upper limit temperature by making
the in-filter pressure lower as the inflowing exhaust gas quantity
becomes smaller, as the filter temperature becomes higher, as the
remaining PM amount becomes larger, and/or as the engine load
becomes higher.
[0087] In view of the above, the ECU 16 is adapted to control the
exhaust throttle valve 12 in such a way as to make the in-filter
pressure lower as the inflowing exhaust gas quantity becomes
smaller, as the filter temperature becomes higher, as the remaining
PM amount becomes larger, and/or as the engine load becomes
higher.
[0088] In the following, a method of controlling the in-filter
pressure during the period in which the high pressure PM filter
regeneration control is performed. In the period in which the high
pressure PM filter regeneration process is performed, the ECU 16
first determines a basic value of the target in-filter pressure
(which will be hereinafter referred to as the basic target
pressure) using as parameters the inflowing exhaust gas quantity
and the remaining PM amount.
[0089] FIG. 2 is a map showing the relationship among the inflowing
exhaust gas quantity Fex, the amount of the particulate matter
trapped on or remaining on the particulate filter (which will be
hereinafter referred to as the remaining PM amount) .SIGMA.PM and
the basic target pressure Pfb.
[0090] In the map shown in FIG. 2, the smaller the inflowing
exhaust gas quantity Fex is, and the larger the remaining PM amount
.SIGMA.PM is, the lower the basic target pressure Pfb is set. In
other words, the larger the inflowing exhaust gas quantity Fex is,
and the smaller the remaining PM amount .SIGMA.PM is, the higher
the basic target pressure Pfb is set.
[0091] Here, as a signal indicative of the inflowing exhaust gas
quantity Fex, the output signal of the air flow meter 6 may be
used. The remaining PM amount Z PM can be determined by subtracting
the product of the PM oxidation rate (that is, the amount of the
particulate matter that is oxidized per unit time) and the time
over which the high pressure PM filter regeneration process has
been performed from the PM trapping amount at the time of starting
the PM filter regeneration process.
[0092] The higher the filter temperature is, and the larger the
inflowing exhaust gas quantity (or the quantity of oxygen flowing
into the particulate filter 11), the higher the PM oxidation rate
is. Therefore, the PM oxidation rate can be determined based on the
filter temperature and the inflowing exhaust gas quantity as
parameters. In connection with this, as a signal indicative of the
filter temperature, the output signal of the exhaust temperature
sensor 13 may be used.
[0093] The PM oxidation rate is also affected by the in-filter
pressure in addition to the filter temperature and the inflowing
exhaust gas quantity. Therefore, the PM oxidation rate increases as
the in-filter pressure becomes higher even if the filter
temperature and the inflowing exhaust gas quantity are the
same.
[0094] In view of this, in this embodiment the ECU 16 is adapted to
correct the PM oxidation rate that is obtained based on the filter
temperature and the inflowing exhaust gas quantity (which rate will
be hereinafter referred to as the basic PM oxidation rate), based
on the in-filter pressure.
[0095] FIG. 3 is a map showing the relationship between the
in-filter pressure Pf and a value called pressure correction
coefficient .alpha.. In the map shown in FIG. 3, the pressure
correction coefficient .alpha. is a value equal to or larger than 1
and set in such a way that the higher the in-filter pressure Pf is,
the larger the value of the pressure correction coefficient .alpha.
is.
[0096] The ECU 16 determines the pressure correction coefficient
.alpha. in accordance with the map shown in FIG. 3, and computes
the PM oxidation rate by multiplying the aforementioned basic PM
oxidation rate by the pressure correction coefficient .alpha.
(basic PM oxidation amount.times..alpha.).
[0097] Using the PM oxidation rate thus determined, it is possible
to estimate the remaining PM amount with high accuracy. Although a
case in which the basic PM oxidation rate determined by the filter
temperature and the inflowing exhaust gas quantity is corrected
based on the in-filter pressure has been described in connection
with this embodiment, the relationship among the filter
temperature, the inflowing exhaust gas quantity, the in-filter
pressure and the PM oxidation rate may be prepared in advance in
the form of a map, alternatively.
[0098] Next, the ECU 16 determines a target value of the in-filter
pressure (which will be hereinafter referred to as the target
pressure) Pft by correcting the basic target pressure Pfb based on
the filter temperature and the engine load.
[0099] FIG. 4 is a map used for determining a correction
coefficient A associated with the filter temperature Tempf (which
coefficient will be hereinafter referred to as the temperature
correction coefficient). In the map of FIG. 4, the temperature
correction coefficient A is a positive number equal to or smaller
than 1, and the higher the filter temperature Tempf is, the lower
the temperature correction coefficient A is set.
[0100] FIG. 5 is a map for determining a correction coefficient B
associated with the engine load Accp (which coefficient will be
hereinafter referred to as the load correction coefficient). As a
signal indicative of the engine load Accp, the output signal of the
accelerator position sensor 17 may be used. In the map of FIG. 5,
the load correction coefficient B is a positive number equal to or
smaller than 1, and the higher the engine load Accp is, the lower
the load correction coefficient B is set.
[0101] The ECU 16 determines the basic target pressure Pfb, the
temperature correction coefficient A and the load correction
coefficient B based on the maps shown in FIGS. 2 to 5, and in
addition computes the target pressure Pft by multiplying the basic
target pressure Pfb by the temperature correction coefficient A and
further by the load correction coefficient B (Pfb.times.A.times.B).
Then, the ECU 16 adjusts the degree of opening of the exhaust
throttle valve 12 in such a way as to make the actual in-filter
pressure Pf equal to the aforementioned target pressure Pft.
[0102] If the adjustment of the degree of opening of the exhaust
throttle valve 12 is performed in the above described manner
repeatedly while the high pressure PM filter regeneration process
is executed, the in-filter pressure is reduced when there is a
possibility that the filter temperature will rise to the upper
limit temperature, such as when the inflowing exhaust quantity is
small, when the filter temperature is high, when the remaining PM
amount is large, and/or when the engine load is high. On the other
hand, the in-filter pressure is increased when the possibility that
the filter temperature will rise to the upper limit temperature is
low, such as when the inflowing exhaust gas quantity is large, when
the filter temperature is low, when the remaining PM amount is
small, and/or when the engine load is low. Thus, the prediction
means and the pressure decreasing means in the present invention
are realized.
[0103] The possibility that the temperature of the particulate
filter 11 rises excessively becomes high when the inflowing exhaust
gas quantity is excessively small, when the filter temperature is
close to the upper limit temperature, when the remaining PM amount
is excessively large, or when the engine load is excessively high.
Therefore, it is preferred that the ECU 16 be adapted to stop, in
such cases, the high pressure PM filter regeneration process
(namely, to adjust the degree of opening of the exhaust throttle
valve 12 back to a normal degree of opening) immediately.
[0104] FIGS. 6 and 7 are maps that define conditions for stopping
the high pressure PM filter regeneration process. Firstly, FIG. 6
is a map that defines a prohibition condition that is defined in
terms of the inflowing exhaust gas quantity Fex, the remaining PM
amount .SIGMA.PM and the filter temperature Tempf as parameters. In
the case shown in FIG. 6, if the point specified by the inflowing
exhaust gas quantity Fex and the remaining PM amount .SIGMA.PM
falls within the area below a boundary line (L1, . . . , Ln: n is
an integer) that is set for each filter temperature Tempf, the high
pressure PM filter regeneration process is stopped. Each of the
boundary lines L1 to Ln is set in such a way that the high pressure
PM filter regeneration process is stopped when the inflowing
exhaust gas quantity is small and the remaining PM amount .SIGMA.PM
is large.
[0105] The boundary line L1 for the filter temperature Tempf of A
is set in such a way that the high pressure PM filter regeneration
process is stopped when the inflowing exhaust gas is larger and the
remaining PM amount is smaller than the corresponding conditions
defined by the boundary line Ln for the filter temperature Tempf of
B (smaller than A).
[0106] FIG. 7 is a map that defines a prohibition condition in
terms of the engine load Accp and the engine speed Ne as
parameters. If the degree of opening of the exhaust throttle valve
12 is set low when the engine load Accp is high, the possibility
that the filter temperature Tempf will reach the upper limit
temperature becomes high and it is possible that the drivability is
deteriorated. When the engine speed Ne is high to a certain extent,
the exhaust gas quantity discharged from the internal combustion
engine 1 is large. In such a state, if the degree of opening of the
exhaust throttle valve 12 is set low, there is a possibility that
the in-filter pressure Pf becomes excessively high. Therefore, in
the case shown in FIG. 7, the condition is set in such a way that
the high pressure PM filter regeneration process is stopped in the
area in which the engine load Accp is high and the engine speed Ne
is high.
[0107] In some cases, the running condition of the internal
combustion engine 1 enters the region in which fuel cut is to be
effected, while the high pressure PM filter regeneration process is
being performed in the above-described way. If fuel cut is effected
in the state in which the degree of opening of the exhaust throttle
valve 12 is set low, unnecessary exhaust brake acts on the internal
combustion engine 1. This may possibly deteriorate the
drivability.
[0108] One method for avoiding this is to adjust the degree of
opening of the exhaust throttle valve 12 back to a normal degree of
opening as long as fuel cut is performed. By adjusting the degree
of opening of the exhaust throttle valve 12 back to the normal
degree of opening during the fuel cut period, it is possible to
prevent unnecessary exhaust brake from acting. In this case,
however, a large quantity of low temperature air passes through the
particulate filter 11, and there is a possibility that the
temperature of the particulate filter 11 becomes lower than
temperatures that enable oxidation of particulate matter.
[0109] If the temperature of the particulate filter 11 becomes
lower than temperatures that enable oxidation of particulate matter
while fuel cut is being performed, it is necessary, upon restarting
the PM filter regeneration process after fuel cut is ended, to
raise the temperature of the particulate filter 11 again up into
the temperature region in which the oxidation of the particulate
matter is possible. This may leads to disadvantages such as a
decrease in gas mileage.
[0110] In view of this, in the PM filter regeneration control in
this embodiment, the ECU 16 is adapted to continue, when the
running condition of the internal combustion engine enters the
region in which fuel cut is to be effected while the high pressure
PM filter regeneration process is being performed, fuel injection
to inject a certain quantity of fuel without effecting fuel
cut.
[0111] By continuing fuel injection to inject a certain quantity
(Qf/c) of fuel in the state in which fuel cut is to be effected
while the high pressure PM filter regeneration process is
performed, it is possible to prevent deterioration in the
drivability, since a torque that cancels the exhaust brake is
generated by the internal combustion engine 1. In addition, since
the temperature of the exhaust gas is kept high by injection of a
certain quantity of fuel, it is possible to oxidize the particulate
matter trapped on the particulate filter 11 even in the state in
which fuel cut is to be effected.
[0112] Since the higher the in-filter pressure Pf is, the larger
the braking force acting on the internal combustion engine 1
becomes, it is preferred that the higher the in-filter pressure Pf
is, the larger the aforementioned fuel injection quantity Qf/c be
made, as shown in FIG. 8.
[0113] If the fuel injection quantity Qf/c is increased/decreased
in proportion to the in-filter pressure Pf, the internal combustion
engine 1 produces a torque proportional to the braking force of the
exhaust brake. Therefore, deterioration in the drivability can be
prevented.
[0114] As per the above, the fuel injection means in the present
invention is realized by adjusting the fuel injection quantity
through the fuel injection valve 3 to the fuel injection quantity
Qf/c proportional to the in-filter pressure Pf, under a control by
the ECU 16, when the running condition of the internal combustion
engine enters the region in which fuel cut is to be effected while
the high pressure PM filter regeneration process is being
performed.
[0115] In the following, the high pressure PM filter regeneration
process in this embodiment will be described with reference to
FIGS. 9 to 12. FIG. 9 is a flow chart of a high pressure PM filter
regeneration routine. FIG. 10 is a flow chart of a remaining PM
amount calculation routine. FIG. 11 is a flow chart of a fuel cut
control routine. The high pressure PM filter regeneration routine,
the remaining PM amount calculation routine and the fuel cut
control routine are stored in advance in a ROM of the ECU 16, and
executed by the ECU 16 repeatedly at regular intervals.
[0116] First, in the high pressure PM filter regeneration routine
shown in FIG. 9, a determination is made by the ECU 16 in step S101
as to whether the PM filter regeneration process is currently
performed or not.
[0117] If the question in step S101 is answered in the negative,
the process of the ECU 16 proceeds to step S106, where the degree
of opening of the exhaust valve 12 is adjusted to the normal degree
of opening, and then execution of this routine is once
terminated.
[0118] If the question in step S101 is answered in the affirmative,
the process of the ECU 16 proceeds to step S102. In step S102, the
ECU 16 reads in the inflowing exhaust gas quantity Fex (i.e. the
output signal of the air flow meter 6) the remaining PM amount
.SIGMA.PM, the filter temperature Tempf (i.e. the output signal of
the exhaust gas temperature sensor 13), the engine load Accp (i.e.
the output signal of the accelerator position sensor 17), the
engine speed Ne and the in-filter pressure Pf (i.e. the output
signal of the exhaust gas pressure sensor 14).
[0119] The remaining PM amount .SIGMA.PM mentioned above is
calculated by the remaining PM amount calculation routine shown in
FIG. 10. In the remaining PM amount calculation routine, firstly in
step S201, a determination is made by the ECU 16 as to whether the
PM filter regeneration process is currently performed or not.
[0120] If the question in step S201 is answered in the negative,
the ECU 16 once terminates execution of this routine. If the
question in step S201 is answered in the affirmative, the ECU 16
reads in, in step S202, the inflowing exhaust gas quantity Fex
(i.e. the output signal of the air flow meter 6), the filter
temperature Tempf (i.e. the output signal of the exhaust gas
temperature sensor 13), and the in-filter pressure Pf (i.e. the
output signal of the exhaust gas pressure sensor 14).
[0121] In step S203, the ECU 16 computes the basic PM oxidation
rate .DELTA..SIGMA.PMb using as parameters the inflowing exhaust
gas quantity Fex and the filter temperature Tempf that have been
read in step S202.
[0122] In step S204, the ECU 16 computes the pressure correction
coefficient .alpha. based on the in-filter pressure Pf that has
been read in step S202 and the map of FIG. 3 described before.
[0123] In step S205, the ECU 16 computes the PM oxidation rate
.DELTA..SIGMA.PM by multiplying the basic PM oxidation rate
.DELTA..SIGMA.PMb obtained in step S203 by the pressure correction
coefficient .alpha. obtained in step S202
(.alpha..SIGMA.PM=.alpha..SIGMA.PMb.times..alpha.).
[0124] In step S206, the ECU 16 computes the amount of the
particulate matter that has been oxidized since the latest previous
execution of this routine until now by multiplying the PM oxidation
rate .DELTA..SIGMA.PM obtained in step S205 by the time t elapsed
since the latest previous execution of this routine until now
(.DELTA..SIGMA.PM.times.t). Subsequently, the ECU 16 computes the
current remaining PM amount .DELTA..SIGMA.PM by subtracting the
aforementioned amount of particulate matter
.DELTA..SIGMA.PM.times.t from the previous remaining PM amount
.DELTA..SIGMA.PMold computed in the latest previous execution of
this routine (.DELTA..SIGMA.PMold-.DELTA..SIGMA.PM.times.t).
[0125] Referring back to the high pressure PM filter regeneration
routine shown in FIG. 9, in step S103, a determination is made by
the ECU 16 as to whether or not the condition for stopping the high
pressure PM filter regeneration process is met based on the
inflowing exhaust gas quantity Fex, the filter temperature Tempf,
the remaining PM amount .SIGMA.PM, and the engine load Accp that
have been read in step S102 as parameters.
[0126] Specifically, a determination is made by the ECU 16 as to
whether or not the condition of the particulate filter 11 is in the
region in which the high pressure PM filter regeneration process is
to be stopped, based on the inflowing exhaust gas quantity Fex, the
filter temperature Tempf, the remaining PM amount .SIGMA.PM and the
above described map of FIG. 6. In addition, a determination is made
by the ECU 16 as to whether or not the engine load Accp is in the
region in which the high pressure PM filter regeneration process is
to be stopped, based on the engine load Accp and the above
described map of FIG. 7.
[0127] If it is determined that the condition of the particulate
filter 11 is in the region in which the high pressure PM filter
regeneration process is to be stopped and/or that the engine load
Accp is in the region in which the high pressure PM filter
regeneration process is to be stopped, the process of the ECU 16
proceeds to step S106. In step S106, the ECU 16 controls the degree
of opening of the exhaust throttle valve 12 to the normal degree of
opening.
[0128] In this case, with stoppage of the high pressure PM filter
regeneration process, excessive temperature rise of the particulate
filter 11 and deterioration in the drivability of the internal
combustion engine 1 are prevented from occurring.
[0129] On the other hand, if it is determined that the condition of
the particulate filter 11 is not in the region in which the high
pressure PM filter regeneration process is to be stopped and the
engine load Accp is not in the region in which the high pressure PM
filter regeneration process is to be stopped, it is considered that
the condition for stopping the high pressure PM filter regeneration
process is not met, and the process of the ECU 16 proceeds to step
S104.
[0130] In step S104, the ECU 16 determines a target pressure Pft by
computation. Specifically, the ECU 16 computes the target pressure
Pft based on the inflowing exhaust gas quantity Fex, the remaining
PM amount .SIGMA.PM, the filter temperature Tempf, and the engine
load Accp using the maps of FIGS. 2, 4 and 5, as described
before.
[0131] In step S105, the ECU 16 controls the degree of opening of
the exhaust throttle valve 12 in such a way that the actual
in-filter pressure Pf (i.e. the output signal of the exhaust gas
pressure sensor 14) becomes equal to the target pressure Pft
mentioned above.
[0132] For example, the ECU 16 calculates a difference .DELTA.Pf
(=Pft-Pf) by subtracting the actual in-filter pressure Pf from the
target pressure Pft. Then, the ECU 16 determines a degree of
opening correction amount .DELTA..theta. for the exhaust throttle
valve 12 from the aforementioned difference .DELTA.Pf and the map
presented as FIG. 12.
[0133] In the map of FIG. 12, when the aforementioned difference
.DELTA.Pf is positive (namely, Pft>Pf), the degree of opening
correction amount .DELTA..theta. has a negative value, and it is
set in such a way that the larger the aforementioned difference
.DELTA.Pf is, the smaller the degree of opening correction amount
.DELTA..theta. is (i.e. the larger the absolute value
|.DELTA..theta.| is). On the other hand, when the aforementioned
difference .DELTA.Pf is negative (namely, Pft<Pf), the degree of
opening correction amount .DELTA..theta. has a positive value, and
it is set in such a way that the smaller the aforementioned
difference .DELTA.Pf is, the larger the degree of opening
correction amount .DELTA..theta. is (i.e. the larger the absolute
value |.DELTA..theta.| is).
[0134] After the degree of opening correction amount .DELTA..theta.
for the exhaust throttle valve 12 has been determined based on the
difference .DELTA.Pf and the map shown in FIG. 12, the ECU 16
controls the exhaust throttle valve 12 to change the degree of
opening of the exhaust throttle valve 12 by an amount equal to that
degree of opening correction amount .DELTA..theta. (where the
degree of opening of the valve is increased when .DELTA..theta. is
positive, and decreased when .DELTA..theta. is negative).
[0135] By repeated execution of the routines shown in FIGS. 9 and
10 by the ECU 16 while the high pressure PM filter regeneration
process is performed, the in-filter pressure Pf is made lower when
there is a possibility that the filter temperature will rise to the
upper limit temperature as is the case when the inflowing exhaust
gas quantity Fex is small, when the filter temperature Tempf is
high, when the remaining PM amount .SIGMA.PM is large and/or when
the engine load Accp is high. Accordingly, it is possible to
perform the high pressure PM filter regeneration process while
suppressing excessive temperature rise of the particulate filter
11, even while the vehicle is moving. On the other hand, when the
possibility that the filter temperature will rise to the upper
limit temperature is low as is the case when the inflowing exhaust
gas quantity is large, when the filter temperature is low, when the
remaining PM amount is small and/or when the engine load is low,
the in-filter pressure Pf becomes high. Therefore, it is possible
to shorten the time required for executing the PM filter
regeneration process.
[0136] Next, referring the fuel cut control routine shown in FIG.
11, a determination is made by the ECU 16 in step S301 as to
whether or not the condition for performing fuel cut is met. The
condition for performing fuel cut may be, for example, that the
degree of opening of the accelerator (that is, the output signal of
the accelerator position sensor 17) is zero and the engine speed is
higher than a predetermined speed.
[0137] If the question in step S301 is answered in the negative,
the ECU 16 once terminates execution of this routine. On the other
hand, if the question in step S301 is answered in the affirmative,
the process of the ECU 16 proceeds to step S302.
[0138] In step S302, a determination is made by the ECU 16 as to
whether or not the high pressure PM filter regeneration process is
currently performed. If the question in step S302 is answered in
the negative, the ECU 16 controls to perform fuel cut (namely, to
stop fuel injection) in step S306, and terminates execution of this
routine. On the other hand, if the question in step S302 is
answered in the affirmative, the process of the ECU 16 proceeds to
step S303. In step S303, the ECU 16 reads in the in-filter pressure
(namely, the output signal of the exhaust gas pressure sensor 14)
Pf.
[0139] In step S304, the ECU 16 computes the fuel injection
quantity Qf/c based on the in-filter pressure Pf read in step S303
and the map of FIG. 8 described before.
[0140] In step S305, the ECU 16 causes the fuel injection valve to
inject fuel with the fuel injection quantity Qf/c computed in the
above described step S304.
[0141] By continuing fuel injection with the quantity Qf/c that is
determined in relation to the in-filter pressure Pf without
performing fuel cut even if the condition for performing fuel cut
is met while the high pressure PM filter regeneration process is
performed, it is possible to prevent unnecessary exhaust brake from
acting. In addition, it is thereby possible to keep the filter
temperature Tempf within the temperature range in which oxidation
of particulate matter is possible.
[0142] Therefore, it is possible to prevent deterioration in the
drivability and to continue the high pressure PM filter
regeneration process even if the condition for performing fuel cut
is met while the high pressure PM filter regeneration process is
performed.
[0143] According to the embodiment described in the foregoing, it
is possible to perform the high pressure PM filter regeneration
process while preventing excessive temperature rise of the
particulate filter 11 even when the running conditions of the
internal combustion engine 1 can easily change as is the case when
the vehicle is moving, and in addition, it is possible to prevent
deterioration in the drivability caused by the high pressure PM
filter regeneration process.
Second Embodiment
[0144] Next, a second embodiment of the exhaust gas purification
system according to the present invention will be described with
reference to FIGS. 13 to 14. Here, only structures that are
different from the above described first embodiment will be
described, and descriptions of structures similar to those in the
first embodiment will be omitted.
[0145] FIG. 13 is a diagram schematically showing the structure of
an internal combustion engine 1 according to this embodiment. In
FIG. 13. a flow rate regulation valve 18 is provided in the exhaust
passage 9 upstream of the particulate filter 11. The flow rate
regulation valve 18 is adapted to be controlled electrically by the
ECU 16. In addition, an exhaust brake switch 19 is connected to the
ECU 16.
[0146] When the exhaust brake switch 19 is turned on, the ECU 16
controls to decrease the degree of opening of the exhaust throttle
valve 12. A decrease in the degree of opening of the exhaust
throttle valve 12 leads to an increase in frictions acting on the
internal combustion engine 1 due to an increase in the exhaust gas
pressure, whereby a braking force (namely, exhaust brake) acts on
the internal combustion engine 1.
[0147] When the degree of opening of the exhaust throttle valve 12
is further increased while the high pressure PM filter regeneration
process is performed in order to activate exhaust brake, there is a
possibility that the in-filter pressure Pf rises excessively and,
at the same time, that the inflowing exhaust gas quantity Fex
decreases excessively. If the in-filter pressure Pf becomes
excessively high and the inflowing exhaust gas quantity Fex becomes
excessively small simultaneously, the possibility that the
temperature of the particulate filter 11 rises excessively becomes
high due to the combined effect of an increase in the particulate
matter oxidation rate and a decrease in the quantity of heat that
is carried away from the particulate filter 11 by the exhaust
gas.
[0148] In view of this, in this embodiment when the exhaust brake
switch 19 is turned on while the high pressure PM filter
regeneration process is being performed, a prediction is made by
the ECU 16 as to whether or not there is a possibility that the
temperature of the particulate filter 11 will rise excessively if
exhaust brake is activated (namely, if the in-filter pressure is
increased).
[0149] For example, it is predicted by the ECU 16 that there is a
possibility that the temperature of the particulate filter 11 will
rise excessively if exhaust brake is activated when at least one of
the following conditions is met: (1) the inflowing exhaust gas
quantity Fex is smaller than a predetermined flow rate; (2) the
remaining PM amount .SIGMA.PM is larger than or equal to a
predetermined PM amount; and (3) the filter temperature Tempf is
larger than or equal to a predetermined temperature. On the other
hand, if none of the above described conditions (1) to (3) are met,
it is predicted by the ECU 16 that there is no possibility that the
temperature of the particulate filter 11 will rise excessively if
exhaust brake is activated.
[0150] In connection with the above, the ECU 16 may use a map shown
in FIG. 14 in making a determination as to whether or not there is
a possibility that the temperature of the particulate filter 11
will rise excessively. The map shown in FIG. 14 defines, in terms
of the inflowing exhaust gas quantity Fex, the remaining PM amount
Z PM and the filter temperature Tempf as parameters, the region in
which reduction of the degree of opening of the exhaust throttle
valve 12 is prohibited (the exhaust throttling prohibition region).
In FIG. 14, when the point specified by the inflowing exhaust gas
quantity Fex and the remaining PM amount .SIGMA.PM falls within the
area below a boundary line (M1, . . . , Mn: n is an integer) that
is set for each filter temperature Tempf, reduction of degree of
opening of the exhaust throttle valve 12 is prohibited. When it is
determined based on such a map that reduction of the degree of
opening of the exhaust throttle valve 12 is to be prohibited, the
ECU 16 regards that there is a possibility that the temperature of
the particulate filter 11 will rise excessively if exhaust brake is
activated by reducing the degree of opening of the exhaust throttle
valve 12.
[0151] When it is predicted by the above described method that
there is no possibility that the temperature of the particulate
filter 11 will rise excessively, the ECU 16 controls to activate
exhaust brake by reducing the degree of opening of the exhaust
throttle valve 12. On the other hand, when it is predicted that
there is a possibility that the temperature of the particulate
filter 11 will rise excessively, the ECU 16 controls to activate
exhaust brake by reducing the degree of opening of the flow rate
regulation valve 18.
[0152] By selectively utilizing the exhaust throttle valve 12 and
the flow rate regulation valve 18 to activate exhaust brake, it is
possible to activate exhaust brake while preventing an excessive
temperature rise of the particulate filter 11.
[0153] In the following, an exhaust brake control process in this
embodiment will be described with reference to FIG. 15. FIG. 15 is
a flow chart of an exhaust brake control routine. The exhaust brake
control routine is stored in advance in the ROM of the ECU 16 and
executed repeatedly by the ECU 16 at certain regular intervals.
[0154] In the exhaust brake control routine, firstly in step S401,
a determination is made by the ECU 16 as to whether the exhaust
brake switch 19 is on or not.
[0155] If the question in step S401 is answered in the negative,
the ECU 16 once terminates execution of this routine. On the other
hand, if the question in step S401 is answered in the affirmative,
the process of the ECU 16 proceeds to step S402.
[0156] In step S402, a determination is made by the ECU 16 as to
whether or not the PM filter regeneration process (either the high
pressure PM filter regeneration process or the normal PM filter
regeneration process) is currently performed. If the question in
step S402 is answered in the negative (namely, if neither the high
pressure PM filter regeneration process nor the normal PM filter
regeneration process is performed), the process of the ECU 16
proceeds to step S406, where the ECU 16 controls to activate
exhaust brake by reducing the degree of opening of the exhaust
throttle valve 12.
[0157] On the other hand, if the question in step S402 is answered
in the affirmative, the process of the ECU 16 proceeds to step
S403, where the ECU 16 reads in the inflowing exhaust gas quantity
Fex, the remaining PM amount .SIGMA.PM and the filter temperature
Tempf.
[0158] In step S404, a prediction is made by the ECU 16 as to
whether or not there is a possibility that the temperature of the
particulate filter 11 will rise excessively if exhaust brake is
activated by reducing the degree of opening of the exhaust throttle
valve 12, based on the inflowing exhaust gas quantity Fex, the
remaining PM amount .SIGMA.PM and the filter temperature Tempf that
have been read in step S403.
[0159] If it is predicted in step S404 that there is no possibility
that the temperature of the particulate filter 11 will rise
excessively, the process of the ECU 16 proceeds to step S406. In
step S406, the ECU 16 reduced the degree of opening of the exhaust
throttle valve 12 to activate exhaust brake.
[0160] On the other hand, if it is predicted in step S404 that
there is a possibility that the temperature of the particulate
filter 11 will rise excessively, the process of the ECU 16 proceeds
to step S405.
[0161] In step S405, the ECU 16 controls to reduce the degree of
opening of the flow rate regulation valve 18. In this case, since
the exhaust gas pressure in the upstream of the flow rate
regulation valve 18 increases, and the exhaust gas pressure in the
downstream of the flow rate regulation valve 18 decreases, it is
possible to activate exhaust brake while reducing the in-filter
pressure Pf. This means that, it is possible to activate exhaust
brake while preventing excessive temperature rise of the
particulate filter 11.
[0162] As per the above, the exhaust brake means in the present
invention is realized by the ECU 16 which executes the exhaust
brake control routine. Accordingly, it is possible to activate
exhaust brake while preventing excessive temperature rise of the
particulate filter 11 even while the high pressure PM filter
regeneration process is being performed.
[0163] In the above described first and the second embodiments,
cases in which the in-filter pressure is reduced while the high
pressure PM filter regeneration process is performed by increasing
the degree of opening of the exhaust throttle valve 12 have been
described. However the way of reducing the in-filter pressure is
not only that.
[0164] Alternatively, for example, the in-filter pressure may be
reduced by decreasing the degree of opening of the intake throttle
valve 8. In this case, the quantity of the exhaust gas flowing into
the particulate filter 11 decreases with a decrease in the quantity
of the intake air, and hence the in-filter pressure decreases.
[0165] In the case of an internal combustion engine equipped with
an EGR passage for recirculating the exhaust gas from the exhaust
passage upstream of the particulate filter to the intake passage
and an EGR valve for regulating the gas flow through the EGR
passage, the in-filter pressure may be reduced by increasing the
degree of opening of the EGR valve. In this case, the quantity of
the exhaust gas flowing into the particulate filter decreases with
an increase in the quantity of the EGR gas, and hence the in-filter
pressure decreases.
[0166] In the case of an internal combustion engine equipped with a
bypass passage for guiding the exhaust gas from the exhaust passage
upstream of the particulate filter to the exhaust passage
downstream of the exhaust throttle valve and a flow rate regulation
valve for regulating the gas flow through the bypass passage, the
in-filter pressure may be reduced by increasing the degree of
opening of the flow rate regulation valve. In this case, the
quantity of the exhaust gas flowing into the particulate filter
decreases with an increase in the flow rate of the exhaust gas that
flows detouring around the particulate filter and the exhaust
throttle valve, and hence the in-filter pressure decreases.
[0167] In the case of an internal combustion engine equipped with a
variable volume type centrifugal supercharger, the in-filter
pressure may be reduced by increasing the volume of the centrifugal
supercharger. In this case, the intake air quantity decreases with
a decrease in the supercharging pressure, and hence the quantity of
the exhaust gas flowing into the particulate filter decreases. As a
result, the in-filter pressure decreases.
[0168] While the invention has been described in terms of preferred
embodiments, those skilled in the art will recognize that the
invention can be practiced with modifications within the spirit and
scope of the appended claims.
INDUSTRIAL APPLICABILITY
[0169] According to the present invention, it is possible to
perform the high pressure PM filter regeneration process while
suppressing excessive temperature rise of the particulate filter
even while running conditions of the internal combustion engine can
easily change as is the case when the vehicle is moving.
* * * * *